Despite Massachusetts’ historic leadership on pay equity ­— in 1945 it became the first state to require equal pay for comparable work —­ the gap between men’s and women’s salaries here is now among the biggest in the country.

Women earned 77 percent of what men took home in median full-time pay, placing Massachusetts 37th among states and the District of Columbia, according to 2011 US Census Bureau data analyzed by the American Association of University Women.

That puts Massachusetts behind every other New England state, according to the analysis. The disparity exists despite a highly educated female workforce in the Bay State.

“We are a progressive state and we do all these progressive things,” said Ellie Adair, director of the Massachusetts chapter of the National Organization for Women. “But we are still victim to the same social and cultural forces as everyone else in the country.”

Women working full time in Massachusetts earned a median annual salary of $46,185 in 2011. That was nearly $10,000 more than the median income for women nationwide, but considerably less than the take-home pay of Massachusetts men whose annual median salary was $60,264,according the census data.

On the campaign trail this fall, equal pay for women became a main issue, providing fodder for commercials by Senator-elect Elizabeth Warren and giving rise to Mitt Romney’s “binders-full-of-women” defense.

Critics charge that much of the wage gap in Massachusetts and nationally owes largely to women’s choices — to become mothers and to work in less remunerative fields, such as nursing or teaching.

In Massachusetts, more women delay motherhood until later in life, meaning that more women delay time off from the workplace as well as transition into jobs with greater flexibility — factors that can imbalance men and women’s pay.

A greater percentage of Massachusetts women, also, earn bachelor’s and graduate degrees than women nationwide, an accomplishment that leads to higher-paid jobs and which long was assumed to be a step on the ladder to commensurate pay with men.

“There was a belief in the 1980s that if you dressed for success, that would work,” said Victoria Budson, chair of the Massachusetts Commission on the Status of Women “In the 1990s education was supposed to be the great equalizer.”

Evidence now shows that higher levels of education can make the pay gap more extreme.

Women with more education who land in professional jobs — like doctoring, lawyering or business — encounter wages that are subject to the choices of managers and thus, potentially, unconscious bias and other factors, said Deborah Thompson Eisenberg, a law professor at the University of Maryland Francis King Carey School of Law.

“Lower-wage workers tend to work in jobs where the pay scale is fairly defined and there’s no discretion by a boss to increase or decrease it for subjective reasons,” Eisenberg said. “In upper-level jobs, you may see a set salary but more discretionary pay like stock options and bonuses. That’s where you see disparities.”

Thompson said salary discretion also favors men’s negotiating skills, which tend to be more effective than women’s, yielding higher starting salaries for men, who in Massachusetts also hold a high number of professional jobs.

The US Bureau of Labor Statistics showed that in 2010, female lawyers earned 77.1 percent of what their male counterparts earned, female physicians and surgeons 71 percent, and female operations managers 71.8 percent. By contrast, female food prep workers made 94.1 percent of what their male peers made and receptionists 96.7. percent.

Specialists also note that at the higher end of the pay scale, wages are rarely hourly or union-negotiated, thus women are less likely to know what male counterparts earn. In turn, they are less likely to know they earn less and less likely to advocate for more pay.

“As you get up into industries that require an MBA or JD, there is less transparency in the process,” said Budson, who is also executive director of the Women and Public Policy Program at Harvard Kennedy School of Government. “The less transparency in the process and the less clarity, the larger the pay disparity.”

AnnMarie Duchon credits transparency with helping her win a long-fought but ultimately successful battle for equal pay at the University of Massachusetts Amherst.

When she was hired eight years ago to work in disability services at the university, she learned through a published list of salaries that she was being paid a different rate than a male co-worker with similar education and experience. She asked for equal pay and was denied, she said.

Duchon recalled being told by her female manager that “in this sort of work, we are trying to do more with less and that we all had to take one for the team.”

When she received a promotion to associate director of accommodation services, her pay was still less than that co-worker’s, a difference that added up to nearly $12,000 over the course of seven years, she said.

“I was like, this is real. This isn’t a pittance. This is what I pay for a year in day care,” Duchon said.

She complained again and in April she received a pay differential, retroactive to December 2011. University officials confirmed Duchon’s account but declined comment.

“This pretty much shows that this happens all over the place – in private and public, in small ways and big ways,” Duchon said.

A study by the American Association of University Women found that pay disparity hits youthful workers, as well. One year out of college, women graduates earned 80 percent of their male counterparts’ pay, according to the study. Some of the gap was explained by women’s preference for lower-paying jobs, such as teaching.

Yet after accounting for occupation, along with college major, hours worked, and other factors, a 5 percent difference in earnings was still unexplained, most likely due in part to discrimination or gender difference and willingness and ability negotiate salary, the authors concluded.

The wage gap has narrowed markedly since President Kennedy signed the Equal Pay Act in 1963 making it illegal for employers to pay unequal wages to men and women who do substantially the same work. That year, women working full time made 59 cents for every dollar paid to men.

But stalled progress in the last decade has prompted renewed legislative pushes. In 2009, President Obama signed the Lilly Ledbetter Fair Pay Act, which extended the time for filing equal-pay lawsuits. The Paycheck Fairness Act, which has failed in Congress, would require employers to prove that wage differences are driven by business necessity and would bar companies from retaliating against workers who inquire about or disclose pay disparities. Outgoing Senator Scott Brown voted against it, saying the legislation would be a burden on businesses. Warren, the senator-elect, supports the bill.

In Massachusetts, legislators have sought numerous times to update the state equal pay law by more clearly defining “comparable work,” a delin
eation that they say will give courts greater power to assess wage equity claims. The act would define comparable work as positions that “entail comparable skill, effort, responsibility, and working conditions between employees of the opposite sex.”

State Representative Alice Wolf, Democrat of Cambridge and the bill’s sponsor in the House, said, “What this says is that there is a way of defining comparable work and that you have to pay people equally for comparable work.”